Bugfix: Also clear the command parser’s stack upon invalid commands (Thanks helgikrs)

Fixes: #652

testcases/t/120-multiple-cmds.t

@@ -54,4 +54,13 @@ ok(($unused ~~ @{get_workspace_names()}), 'workspace exists after moving');
 
 # TODO: need a non-invasive command before implementing a test which uses ','
 
+################################################################################
+# regression test: 10 invalid commands should not crash i3 (10 is the stack
+# depth)
+################################################################################
+
+cmd 'move gibberish' for (0 .. 10);
+
+does_i3_live;
+
 done_testing;